流动体系中溢流氢在苯加氢催化反应中的作用

在连续常压固定床反应器上考察了 Pt/Al2 O3分别和惰性石英砂、脱铝 Y沸石、WO3/Al2 O3等组成的机械混合物上苯加氢反应的性能。发现虽然 Y沸石本身没有加氢活性 ,但它的加入可以显著提高 Pt/Al2 O3的活性 ,因为在 Pt中心上得到活化的氢可以快速溢流到邻近的沸石颗粒表面的酸中心上 ,并和吸附在其上的苯发生加氢反应生成环己烷和甲基环戊烷。由于深度脱铝的 Y沸石表面酸中心数减少而导致其上的甲基环戊烷的选择性降低。对于 Pt/Al2 O3和 WO3/Al2 O3的机械混合物来说 ,未在流动体系中观察到活性显著提高的现象。

EFFECT OF SPILLOVER HYDROGEN ON HYDROGENATION OF BENZENE IN A FLOW CATALYTIC REACTION SYSTEM

Reactivity of hydrogenation of benzene over the mechanical mixture of Pt/Al_2O_3 with inert silica, dealuminated Y zeolites or WO_3/Al_2O_3 was investigated using a flow microreactor at atmospheric pressure. It was found that the conversion of benzene increased remarkably with the admixing of the dealuminated Y zeolite with Pt/Al_2O_3 catalyst, even if the zeolite itself was inactive. The additional activity of the mechanical mixture can be ascribed to the acid sites on dealuminated Y zeolite, where the activated hydrogen spilt over from the neighboring Pt sites could hydrogenate the adsorbed benzene with the formation of cyclohexane and methylcycloheptane. On the deep dealuminated Y zeolite, the selectivity of methylcyclopentane was observed to be low owing to the comparative small amounts of acid sites on its surface. However, the overall hydrogenation activity of Pt/Al_2O_3 could not be improved to a significant extent by the addition of WO_3/Al_2O_3, which is also considered to be a good acceptor for the spillover hydrogen.